This application relates to a support for a radiation shield in a superconducting magnetic resonance magnet.
In superconducting magnets the magnet windings are situated in a cryostat to thermally isolate the windings from exterior ambient conditions. To achieve the desired degree of thermal isolation, a thermal radiation shield surrounds the windings but is spaced apart therefrom. The shield and magnet are designed to operate at different temperatures with the magnet windings at the coldest temperature. The radiation shield needs to be supported with sufficient stability to withstand shipping loads yet limit heat transfer to the magnet windings.
All MR magnets have thermal shields to reduce the radiation heat input into the magnet windings. The shields are supported from a helium vessel which encloses the magnet windings or from the vacuum vessel. The supports are typically made of low thermal conductivity material such as fiberglass. The radial distance between the helium vessel and the surrounding shield are several inches allowing supports of at least this length.
In a magnet which does not have a helium vessel and relies on a cyrocooler to allow a superconductor winding such as niobium tin to operate superconductively, all the heat inputs from the thermal shield, suspension supports and conduction down the power leads has to be removed by the cryocooler. In a compact magnet design that operates using just a cyrocooler, space between the windings and the shield is limited and conduction heat from the shield supports to the windings which operate at different temperatures will raise the temperature of the windings. The shield supports need a sufficient cross sectional area to withstand the static and dynamic mechanical loads. However, spacers of sufficient cross sectional area having a short length create an excessive heat leak.
It is an object of the present invention to provide a low thermal conductance support operating in compression for a thermal shield in an MR magnet in which the radial distance between shield and the winding support is limited which can carry the shield mass in both static and dynamic modes with low heat leak to the magnet windings.
It is another object of the present invention to provide a low thermal conductance support for a thermal shield in an MR magnet.
It is a further object of the present invention to provide a low thermal conductance support operating in compression for a thermal shield in an MR magnet which allows easy assembly.
It is yet another object of the present invention to provide a low thermal conductance support operating in compression for a thermal shield in an MR magnet which has adjustment capability for moving the shield relative to the magnet windings.